Resonant inertial actuators of vibration-cancelling force generators, such as those used for at least partially cancelling unwanted rotary wing aircraft vibrations, include electronic control systems that regulate electrical drive currents for driving the resonant inertial actuators about a natural resonant frequency. The rotary wing aircraft vibration cancelling electronic control systems include a command input for receiving a command signal and a power amplifier for providing the electrical drive current to the resonant inertial actuator. A feedback system from the resonant inertial actuator to the electronic control system adjusts the electrical drive current based on outputs of the resonant inertial actuator.
The vibration-cancelling force generators are attached to the aircraft machine structure that is subject to the unwanted vibrations. Resonant inertial actuators have a frame for attachment to the machine structure and an electromagnetically driven sprung mass supported by the frame. The sprung mass, which includes an inertial mass connected to the base frame through a resilient coupling, such as flexure plates, is electromagnetically driven by modulating an oriented electromagnetic field so that the sprung mass is oscillated at the natural resonance frequency. The resonance frequency of the sprung mass corresponds to the frequency at which the machine structure is subject to unwanted vibration, and the phase of the sprung mass oscillation is offset with respect to the phase of the unwanted vibration to produce destructive interference.
The command signal can be a variable analog input voltage received by the command input as an instruction to provide a scaled electrical drive current to the resonant inertial actuator. The feedback system, which also connects the resonant inertial actuator to the electronic control system, can monitor both a feedback current through the resonant inertial actuator and a feedback voltage across the inertial actuator. Based on the two feedbacks, the electronic control system can limit the inertial actuator current and voltage to respective maximum values.
When driving the resonant inertial actuator with drive current, significant changes in the force response of the inertial actuator are known to accompany frequency sweeps through the frequency of the inertial actuator's natural resonance. On the other hand, voltage control is known to have a much flatter response in both magnitude and phase through the natural resonance frequency. Near resonance, a weak current loop has been used, which has some voltage-like performance near resonance.
Known resonant inertial actuators have strict design limits for such parameters as voltage, current, force, stroke, power, and temperature. To assure safe and efficient operation within these design limits, resonant inertial actuators are generally designed with considerable “overhead” in their mechanical and electrical design. The overhead, which involves additional design features or scaling to larger sizes or capacities, generally result in heavier and more expensive inertial actuators and actuator controls.